Tightly Coulomb-bound four- and five-particle intervalley states in monolayer tungsten diselenide

Tightly-bound excitonic complexes in atomically-thin semiconducting transition metal dichalcogenides (TMDCs) provide an appealing platform for studying many-body correlations. Here, we present the observation of the Coulomb-bound four-particle biexciton and five-particle exciton-trion in monolayer tungsten diselenide by the photoluminescence (PL) measurements. The ultrahigh quality sample enables us to resolve and assign several intrinsic emission features in the energy window right below the bright neutral exciton emission. Interestingly, we discover that the biexciton consists of a spin-zero bright exciton in one valley and a spin-one ‘‘dark’’ exciton in the other, which is confirmed by the magneto-PL measurements. The binding energy of these multi-particle states are further estimated as 18–23 meV and 13–20 meV for the biexciton and the exciton-trion, respectively, by charge doping and thermal activation measurements. The tightly bound nature of the multi-particle states in atomically-thin TMDCs offer opportunities for understanding many-body physics and for realizing interesting applications such as Bose-Einstein condensation, and quantum communication and teleportation.

Reference: Chen et al, NATURE COMMUNICATIONS | (2018)9:3717